John McCain received the endorsement of George Bush at the White House yesterday, putting the seal on gaining the Republican party's nomination for the November presidential elections.

The endorsement comes eight years after Bush destroyed McCain's hopes of securing the presidency in the 2000 primaries.

On Tuesday McCain swept to victory in four races - Ohio, Texas, Rhode Island and Vermont - which took his delegate count beyond the 1,191 needed to secure the Republican nomination. Mike Huckabee, his last serious rival, backed out of the contest, vowing to inject his energies into the McCain campaign.

The victory of the senator for Arizona marked one of the most remarkable comebacks in US political history. Last summer he was all but written off as a candidate but he turned his controversial support for the troop surge in Iraq to his advantage.

Appearing with McCain in the White House Rose Garden, Bush said: "A while back I don't think many people would have thought that John McCain would be here as the nominee of the Republican party. John showed incredible courage, strength of character and perseverance in order to get to this moment and that's exactly what we need in a president."

McCain has a crucial opportunity to gather his forces over the next few weeks while the Democrats are battling away. The priority will be to refill his campaign coffers to compete with the lavishly funded campaigns of either Barack Obama or Hillary Clinton. "The Democrats will have to spend all their money for weeks to come on beating up on each other," said Whit Ayres, a Republican pollster based in Washington.

McCain will probably continue to put Iraq and security high on the agenda. That could be risky if Iraq slumps back into violence, but with Clinton and Obama attacking each other over national security, they are arguably doing McCain's work for him. McCain will seek to underline his foreign affairs credentials with a trip later this month to Britain, Iraq and Israel.

Early speculation on McCain's running mate centred on Senator Kay Bailey Hutchinson of Texas; Charlie Crist, the governor of Florida, which could be a key state in November; and Huckabee, who would help win over the religious right but is not popular among economic conservatives.